Built-up camshafts, for example with a steel tube as the shaft body, can have various installed or attached parts, namely cams, sprocket mountings, sprockets, axial bearings, axial bearing shoulders, and signal emitters, or the like.
A camshaft is called "built-up" when the shaft body and the cams have been produced separately and wherein the essentially finished cams are fixed on the shaft body, for example by pushing them on. Such built-up camshafts and their assembly are described in German Patent Publications DE 41 21 951 C1 and DE 195 20 306 A1. Within the prior art there are also one-piece camshafts, i.e. with cams shaped integrally on the shafts, which can be cast of iron, for example. The camshafts can also be produced as hollow bodies. Reference is made in this connection to British Letters Patents GB 1 596 442 and GB 1 191 202, Japanese Patent Publication JP-A-619 959 and European Patent Publications EP 0 154 787 B1 and EP 0 272 471 B1. As a rule, cast camshafts are produced in such a way that the cams and other functional elements are cast integrally with the shaft in one piece.
In modern internal combustion engines, for which the camshafts herein described are preferably employed, levers with attached small rollers are actuated with the aid of the cams and not, as was previously done, by straight tappets. The rollers run on the cams. Cams are required for this which not only must be worked very accurately (accuracy at an order of magnitude of micrometers), but which require at least one concave area at the circumference for reasons of the kinematics of the lever linkage. In this connection a "concave" area identifies a cam circumference section with a radius of the cam which is reduced and then again increases via two geometric reversing points. The lever roller runs over the concave circumferential section like a car wheel over a bump. The concave circumferential area should of course also be worked as accurately as the remaining portions of the cam circumference. The present invention is recognition that these prescribed accuracies can only be achieved with economically justifiable means by separately manufactured cams, for example by sintering. If lever linkages are to be actuated by cams, practically only built-up camshafts can be considered.
In actuality camshafts for internal combustion engines are already balanced for vibrational reasons by shaping the shaft, so that at all possible rpm there is optimal quiet running. Such balancing really is out of the question with a built-up camshaft, for example based on a steel tube, since it is not possible to balance a steel tube with economically and safety-wise justifiable means, together with the micrometer accuracy demanded at the same time. Such optimally balanced camshafts are commercially available only in cast iron. But with these camshafts the cams themselves cannot be worked with the accuracy demanded by modern technology as mentioned above.